<div>
    Copies the SSH key file given in the credentials to a temporary location, then sets a variable to that location.
    (The file is deleted when the build completes.) Also optionally sets variables for the SSH key's username and passphrase.
</div>
<div>
    <strong>Warning</strong>: if the Jenkins controller or agent node has multiple executors,
    any other build running concurrently on the same node will be able to read
    the contents of this file.
</div>
